Glucocorticoids (GC) remain the mainstay of therapy for acute MS episodes. However, it is also clear that GC fail to prevent MS relapses and disease progression, and appear to have little effect on long-term T cell responses to myelin antigens in patients. Similarly, GC treatment efficiently down-regulates EAE in rodents, but fails to prevent subsequent relapses. Importantly, GC fail to inhibit proliferation and cytokine production by T cells at inflammatory sites, which could be particularly relevant in the CMS where expression of MIF in a number of cell types including neurons could contribute to this observation. Our own preliminary data and a recent report by Powell and colleagues strongly support a link between MIF and glucocorticoids in EAE. We found that Wt mice show exacerbation of EAE and relapsing disease upon termination of Dexamethasone treatment, but not MIF-/- mice. Furthermore, EAE is substantially exacerbated in MIF-/- mice treated with the glucocorticoid receptor inhibitor Mifepristone (RU-486). Furthermore, the frequencies and functional avidity of myelin-specific T cells were decreased when MIF was neutralized in vivo with anti-MIF antibodies. Based on these results and the literature it is highly likely that MIF interferes with GC-mediated immunosuppression, induction of apoptosis, and/or migration of inflammatory cells to the CMS. This proposal will test the hypothesis that: MIF promotes EAE by counter-regulating the immunosuppressive effects of glucocorticoids on T cell and macrophage apoptosis, effector functions, and CMS migration. This hypothesis will be tested with the following specific aims: Aim 1. To determine whether MIF interferes with glucocorticoid-mediated apoptosis of encephalitogenic T cells and APCs in EAE. Aim 2. To determine whether MIF counter-regulates glucocorticoid-mediated immunosuppression of T cell effector functions in EAE. Aim 3. To determine the mechanism of MIF interference with apoptosis.